The provision of metallic effects in surface coatings, plastics coloration, cosmetic preparations and the like is well known. To achieve this effect, one approach has been to disperse both a metallic pigment and a transparent colored pigment in the composition. The metallic pigment is usually aluminum flake and the colored pigment can be, for instance, iron oxide. The art has also combined the two pigments into a single entity by precipitating the colored material on the aluminum flake.
The precipitation of, for instance, iron oxide on the aluminum flake was often carried out from an aqueous solution but that gave rise to various difficulties. Aluminum readily reacts in aqueous media, very dilute solutions of the iron oxide were required, complexing additives were necessary and the procedure had to be carried out in a limited pH range.
An alternate, non-aqueous procedure is described in U.S. Pat. No. 4,328,042. Here, iron pentacarbonyl is oxidized to iron oxide and carbon dioxide in a fluidized bed of the aluminum flake with oxygen at elevated temperature. To obtain reproducible results, the carbonyl cannot exceed 5 volume percent of the fluidizing gas. The use of the low concentration carbonyl and fluidized bed operation are obvious drawbacks of this approach.
It is desirable to provide a metallic oxide color effect material which has the same or better pigment properties as the products just mentioned but without encountering the production and materials limitations of that prior art. The present invention is directed to satisfying that desire.
The present invention provides an oxide metallic color effect material comprising a platelet-shaped substrate encapsulated with a highly light reflective first layer of silver and a layer of iron oxide. The product, where necessary, can be given a post-treatment for specific attributes such as weather stability, polymeric dispersability and cosmetic compatibility. The method of producing the effect material is also a part of this invention.
It is an object of the present invention to provide novel oxide metallic effect materials which can also be prepared in a reliable, reproducible and technically efficient manner. This object is achieved by an effect material comprising a platelet-shaped substrate coated with (a) a highly light reflective first layer of silver; and (b) an iron oxide layer.
Any encapsulatable smooth platelet can be used as the substrate in this invention. Examples of usable platelets include mica, aluminum oxide, bismuth oxychloride, boron nitride, glass flake, iron oxide-coated glass flake, titanium oxide-coated glass flake, iron oxide-coated mica, silicon dioxide and titanium dioxide-coated mica. The size of the platelet-shaped substrate is not critical per se and can be adapted to the particular use. In general, the particles have average largest major dimensions of about 5-250 microns, in particular 5-100 microns. Their specific free surface area (BET) is in general from 0.2 to 25 m2/g.
The degree of reflectivity for the first encapsulating layer, the highly reflective layer, should be at least about 75% and is preferably at least about 90% reflectivity. This layer is constituted by highly reflective silver.
The thickness of the first layer is not critical so long as it is sufficient to make the layer highly reflective. If desirable, the thickness of the first layer can be varied to allow for some selective transmission of light. The mass percent of this coating can vary considerably because it is directly related to the surface area of the particular substrate being utilized and the thickness necessary to achieve the desired reflectivity. In general, the silver thickness should be at least about 5 nm, preferably from about 10 to 75 nm. A thickness of the silver layer outside of the above-mentioned ranges will typically be either completely opaque or allow for substantial transmission of light.
As a result of the high reflectivity, the silver encapsulated substrate is substantially opaque and much more light is reflected than with conventional effect pigments. The amount of fight reflected in the case of, for instance, iron oxide-coated mica is on the order of about 18% whereas the amount of light in the effect pigment of the instant invention is on the order of 35%.
The effect material of the present invention contains an iron oxide layer directly encapsulated onto the first encapsulating layer. The thickness of this layer can vary considerably. As the thickness increases, interference colors are realized. In general, the layer thickness is about 40 to 200 nm, and preferably about 60 to 180 nm.
If desired, an additional outer layer can be provided. The optional outer encapsulating layer, when present, is a material providing a transparency of about 25-75% transmission. More preferably, one would prefer to have about 40-60% transparency for the outer encapsulating layer. The degree of reflectivity and transparency for the different layers can be determined using a variety of methods such as ASTM method E1347-97, E1348-90 (1996) or F1252-89 (1996), all of which are substantially equivalent for the purposes of this invention.
The material employed as the outer layer can be silver, gold, platinum, palladium, rhodium, ruthenium, osmium, iridium and alloys thereof. Alternatively, the outer layer may also be a metal oxide provided that it is not iron oxide, and may also constitute a nitride or carbide.
The effect materials of the invention are notable for multiple encapsulation of the platelet-shaped substrate. In one embodiment, the first layer and the iron oxide layer are further encapsulated by a selectively transparent outer layer that allows for partial reflection of light directed thereon. Preferably, the outer encapsulating layer is selected from the group consisting of silicon, chromium oxide, a mixed metal oxide, titanium dioxide, titanium nitride and aluminum. More preferably, the outer layer is one or more of the precious metals or alloys.
The optional outer layer is, of course, a part of the optical package. Its thickness can vary but must always allow for partial transparency. For instance, the layer has a preferable thickness of about 5 to 20 nm for silicon; about 2 to 15 nm for aluminum; about 1-15 nm for titanium nitride; about 10 to 60 nm for chromium oxide; about 10-100 nm for titanium dioxide; about 5 to 60 nm for a mixed metal oxide, about 5 to 20 nm for silver; about 3 to 20 nm for gold; about 3-20 nm for platinum; and about 5 to 20 nm for palladium. The metal alloys generally have a similar film thickness compared to the pure metal. It is recognized that a film thickness out of the above range may be applicable depending on the desired effect.
All the encapsulating layers of the effect material of the invention are altogether notable for a uniform, homogeneous, film-like structure that results from the manner of preparation according to the invention.
One advantage of the present invention is that one does not have to start with a traditional metal flake which may have structural integrity problems, hydrogen outgassing problems and a host of other perceived issues (pyrophoric and environmental concerns) typically associated with metal flakes. The substrate provides structural integrity and the silver used in this invention is much more chemically stable than aluminum and generally prefers to be in its non-oxidized metallic ground state. Furthermore, silver can maximize the chromaticity of the reflected color(s) of the end product. In addition, when silver is used as the final (outer) layer of the particle, it may impart electrical conductivity to the effect material, which may be desirable in some applications such as powder coatings.
While the metal layers can be deposited by any known means, they are preferably deposited by electroless deposition or reduction and the non-metal layers preferably by aqueous or non-aqueous sol-gel deposition. An advantage of electroless deposition (Egypt. J. Anal. Chem., Vol. 3, 118-123 (1994)) is that it is a worldwide established chemical technique, not requiring cumbersome and expensive infrastructure compared to other techniques. The electroless deposition technique also allows one to control the degree of reflectivity of light quite accurately and easily by varying the metal film thickness. Additionally, the known procedures are generalized procedures capable of being utilized for coating a variety of surfaces. Furthermore, a layer of iron oxide can also be deposited onto any of the substrates by chemical vapor deposition from an appropriate precursor (The Chemistry of Metal CVD, edited by Toivo T. Kodas and Mark J. Hampden-Smith; VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1994, ISBN 3-527-29071-0) or in an aqueous system utilizing a precursor such as iron nitrate.
The products of the present invention are useful in automotive, cosmetic, industrial or any other application where metal flake, pearlescent pigments or absorption pigments are traditionally used.
In the novel process for preparing the coated platelet-like substrates, the individual coating steps are each effected by known procedures such as by electroless deposition or hydrolysis/condensation of suitable starting compounds in the presence of the substrate particles to be coated. For instance, silver can be deposited from reduction of aqueous salts of the metal, such as AgNO3. Silicon dioxide can be deposited from silicon tetraalkoxides such as tetraethoxysilane, bases such as sodium silicate and halide silanes such as silicon tetrachloride; titanium dioxide from tetraalkoxides such as titanium isopropoxide and titanium tetraethoxide, halide compounds such as titanium tetrachloride and sulfate compounds such as titanium sulfate, titanium nitride from titanium tetrachloride, tetrakis(diethylamido)titanium (TDEAT) and tetrakis(dimethylamido)-titanium (TDMAT); iron oxide from iron carbonyl, iron sulfate, iron nitrate and iron chloride; and chromium oxide from chromium carbonyl and chromium chloride.
In general, the synthesis of the color effect material can be as follows: a platelet material such as mica is suspended while stirring in an aqueous medium. The platelet substrate acts as a carrier substrate. It may, but usually will not, have a contribution or effect on the final optical properties of the particulate. To the suspension is added a metal precursor capable of depositing silver on the substrate by electroless deposition, along with a suitable reducing agent. The resulting highly reflective silver metal coated substrate is filtered and washed. An aqueous solution of an iron salt is added and the pH is changed to deposit the iron oxide on the reflecting layer. Then to the aqueous medium, a metal solution for electroless deposition is added as described above allowing for the deposition of a selectively transparent metal coating. The final particulate product is washed and dried.
The metallic oxide color effect materials of the invention are advantageous for many purposes, such as the coloring of paints, printing inks, plastics, glasses, ceramic products and decorative cosmetic preparations. Their special functional properties make them suitable for many other purposes. A product with a conductive outerlayer, for example, could be used in electrically conductive or electromagnetically screening plastics, paints or coatings or in conductive polymers. The conductive functionality of these effect materials makes them have great utility for powder coating applications.
Products of this invention have an unlimited use in all types of automotive and industrial paint applications, especially in the organic color coating and inks field where deep color intensity is required. For example, these effect pigments can be used in mass tone or as styling agents to spray paint all types of automotive and non-automotive vehicles. Similarly, they can be used on all clay/formica/wood/glass/metal/enamel/ceramic and non-porous or porous surfaces. The effect pigments can be used in powder coating compositions. They can be incorporated into plastic articles geared for the toy industry or the home. These effect pigments can be impregnated into fibers to impart new and esthetic coloring to clothes and carpeting. They can be used to improve the look of shoes, rubber and vinyl/marble flooring, vinyl siding, and all other vinyl products. In addition, these colors can be used in all types of modeling hobbies.
The above-mentioned compositions in which the compositions of this invention are useful are well known to those of ordinary skill in the art. Examples include printing inks, nail enamels, lacquers, thermoplastic and thermosetting materials, natural resins and synthetic resins. Some non-limiting examples include polystyrene and its mixed polymers, polyolefins, in particular, polyethylene and polypropylene, polyacrylic compounds, polyvinyl compounds, for example polyvinyl chloride and polyvinyl acetate, polyesters and rubber, and also filaments made of viscose and cellulose ethers, cellulose esters, polyamides, polyurethanes, polyesters, for example polyglycol terephthalates, and polyacrylonitrile.
For a well-rounded introduction to a variety of pigment applications, see Temple C. Patton, editor, The Pigment Handbook, volume II, Applications and Markets, John Wiley and Sons, New York (1973). In addition, see for example, with regard to ink: R. H. Leach, editor, The Printing Ink Manual, Fourth Edition, Van Nostrand Reinhold (International) Co. Ltd., London (1988), particularly pages 282-591; with regard to paints: C. H. Hare, Protective Coatings, Technology Publishing Co., Pittsburgh (1994), particularly pages 63-288. The foregoing references are hereby incorporated by reference herein for their teachings of ink, paint and plastic compositions, formulations and vehicles in which the compositions of this invention may be used including amounts of colorants. For example, the effect pigment may be used at a level of 10 to 15% in an offset lithographic ink, with the remainder being a vehicle containing gelled and ungelled hydrocarbon resins, alkyd resins, wax compounds and aliphatic solvent. The metallic effect pigment may also be used, for example, at a level of 1 to 10% in an automotive paint formulation along with other pigments which may include titanium dioxide, acrylic lattices, coalescing agents, water or solvents. The effect pigment may also be used, for example, at a level of 20 to 30% in a plastic color concentrate in polyethylene.
In the cosmetic field, the effect materials can be used in all cosmetic and personal care applications subject, of course, to all regulatory requirements. Thus, they can be used in hair sprays, face powder, leg-makeup, insect repellent lotion, mascara cake/cream, nail enamel, nail enamel remover, perfume lotion, and shampoos of all types (gel or liquid). In addition, they can be used in shaving cream (concentrate for aerosol, brushless, lathering), skin glosser stick, skin makeup, hair groom, eye shadow (liquid, pomade, powder, stick, pressed or cream), eye liner, cologne stick, cologne, cologne emollient, bubble bath, body lotion (moisturizing, cleansing, analgesic, astringent), after shave lotion, after bath milk and sunscreen lotion.
For a review of cosmetic applications, see Cosmetics: Science and Technology, 2nd Ed., Eds: M. S. Balsam and Edward Sagarin, Wiley-Interscience (1972) and deNavarre, The Chemistry and Science of Cosmetics, 2nd Ed., Vols 1 and 2 (1962), Van Nostrand Co. Inc., Vols 3 and 4 (1975), Continental Press, both of which are hereby incorporated by reference.